The present invention relates to gas purification for atmospheric pollution prevention and more particularly, to a gas purification catalyst especially intended for purification of exhaust gases including lamp black or soot, odor, noxious compounds, and the like, and generated, for example, from various kinds of household or home use burning and cooking appliances utilizing petroleum, gas, briquet, etc., and manufacturing method for such a catalyst.
Compositions of the exhaust gases developed from the home use appliances, etc., as described above are not the same, but differ according to the appliances employed, and these compositions are, for example, carbon monoxide due to incomplete combustion, hydrocarbons, especially olefin group hydrocarbons in the case of burning appliances, and mainly aliphatic or fatty acid group hydrocarbons and kinds of aldehydes in the case of cooking appliances.
Recently, owing to increased air tightness in buildings following the spread of aluminum sash window frames and tendency to multistory construction of apartment houses, mansions, etc., ventilation of indoor air has become very difficult. Under such circumstances, it is strongly desired to increase safety of the household burning appliances and also to eliminate smoke and odor from exhaust gases generated, for example, during cooking. Meanwhile, in the home use burning appliances, technical innovation is under way for higher performance and lower price, and thus development of catalysts of low cost is essential to cope with such technical progress and state of the market in this line of trade.
Conventionally, various kinds of catalysts have been proposed and put into production for meeting the requirements as described in the foregoing, the outstanding catalysts being precious metal catalysts and metallic oxide catalysts. Among known metal catalysts, platinum, palladium or platinum black have been regarded as particularly suitable. However, platinum catalysts conventionally proposed are generally high in cost, and although the metallic oxide catalysts are cheaper than such platinum catalysts, they are still expensive to be used for the household burning appliances. The high cost of the platinum catalysts is attributable not only to expensiveness of the platinum itself, but to the fact that the alumina molded item to be employed as a carrier is expensive and that the manufacturing process in which platinum is caused to be supported on the carrier is rather complicated. The carrier for the catalysts is not limited to alumina, but heat-resistant, chemically inactive and porous substances such as zircon, schreit-sillimanite, magnesium silicate, aluminosilicate, etc. may be employed as disclosed, for example, in Japanese patent publication Tokkosho 47-50980 although those having alumina as main component are mainly employed for practical use. Meanwhile, catalysts employing porous metal as carrier have also been put into production recently.
The substances to be employed as carrier may be broadly divided into ceramic materials and metallic materials, and various methods have conventionally been proposed for manufacturing such carriers. However, the catalysts produced by employing such carriers have advantages and disadvantages of their own, and are expensive, thus requiring further improvement for application thereof to the home use burning appliances, etc.